The present invention relates generally to microelectromechanical systems, and more particularly to a microelectromechanical system having a platform which can be selectively elevated above a supporting substrate and tilted at large angles with respect to the substrate.
The use of microelectromechanical (MEM) systems has grown in conjunction with the ability to fabricate increasingly complex MEM systems. MEM systems have many applications including in free-space reflective-type optical cross connect switch devices. In such devices, MEM systems fabricated on one or more substrates typically include an optically reflective surface or coating upon a platform that can be tilted with respect to the substrate. Two or more MEM systems are operated to tilt respective platforms thereof with respect to the substrate to provide a reflective optical signal pathway between selected optical ports of the switch. As may be appreciated, the number of side-by-side optical ports that can be reflectively interconnected within such a switch and how close the optical ports can be to the surface of the substrate depend upon a number of factors, including how far each optically reflective platform can be tilted with respect to the substrate.
Accordingly, the present invention provides a MEM system having a platform that may be simultaneously elevated from the substrate on which it is fabricated and tilted with one, two or more degrees of freedom with respect to the substrate in a controlled manner by operating one or more actuator microstructures formed on the substrate that are mechanically coupled with the platform. The term xe2x80x9csubstratexe2x80x9d as used herein means those types of structures that can be handled by the types of equipment and processes that are used to fabricate micro-devices on, within, and/or from the substrate using one or more micro photolithographic patterns. Since the platform lifts up from the surface of the substrate, it may be tilted at large angles (e.g., in excess of forty-five degrees or even in excess of ninety degrees) with respect to the substrate without being restricted by contact between the periphery of the platform and the surface of the substrate.
The MEM system of the present invention can be configured to serve a number of functions where it is necessary to position an optical element at large angles with respect to the substrate. For example, with an optically reflective surface or coating on the platform, multiple MEM systems may be incorporated into a free-space reflective-type optical cross connect switch that requires large tilt angles in order to connect optical ports thereof. The platform may also include other optical elements such as, for example, a diffraction grating, a lens or an optical polarizer depending upon the application in which the MEM system is employed. The platform can also serve as an optical shutter for use in blocking optical signals by tilting the platform into a position where it blocks the path of the optical signals.
According to one aspect of the present invention, a large tilt angle MEM system includes a substrate, a platform formed on the substrate and a lever arm formed on the substrate. The substrate may, for example, be comprised of silicon (e.g., a silicon wafer or a portion thereof). The platform and lever arm may be fabricated on the surface of the substrate in accordance with surface micromachining techniques from multiple patterned layers of monocrystalline or polycrystalline silicon with intervening patterned layers of sacrificial oxide deposited on the substrate.
The entire platform is elevatable to a desired height from the substrate (i.e., no portion of the platform is prevented from being lifted off of the substrate) and may also be pivotably attached to the substrate. In this regard, the MEM system may include a first compliant member (e.g., a spring) attaching the platform to the substrate. The first compliant member attaches the platform to the substrate while permitting the platform to be elevated to the desired height from the substrate. The first compliant member also allows the platform to be tilted with respect to the substrate with at least one degree of freedom.
The lever arm is pivotably attached to the substrate in a manner that permits the lever arm to pivot in at least a first direction (e.g., clockwise or counter-clockwise) with respect to the substrate. The lever arm is also coupled with the platform in a manner such that, in response to pivoting of the lever arm in the first direction, the platform is inclined in at least the first direction. In this regard, the lever arm may be coupled with the platform by a second compliant member (e.g., a spring). Upon pivoting of the lever arm in the first direction, the second compliant member transmits force from the lever arm to the platform both lifting the platform and creating a rotational torque that tilts the platform in the first direction with respect to the substrate. In this regard the second complaint member should be sufficiently rigid both laterally and torsionally. Since the point on the lever arm where the second compliant member is connected may swing through a first arc having a different radius than a second arc through which a point on the platform where the second compliant member is connected swings, the second complaint member should also elongate and contract lengthwise. Pivoting of the lever arm in the opposite direction lowers the platform and declines it from the tilted orientation.
The platform may be attached to the substrate and the lever arm in a manner that provides for a change in an angle of inclination of the platform in the first direction with respect to the substrate which exceeds a change in an angle of pivot of the lever arm in the first direction with respect to the substrate upon pivoting of the lever arm in the first direction with respect to the substrate. In this regard, the platform may be attached to the substrate at a first location and the lever arm may be attached to the platform at a second location and to the substrate at a third location, with the first location being between the second and third locations when the platform is in a non-tilted orientation with respect to the substrate. It is also possible to attach the platform to the substrate and the lever arm in a manner that provides for a change in an angle of inclination of the platform in the first direction with respect to the substrate which is less than a change in an angle of pivot of the lever arm in the first direction with respect to the substrate upon pivoting of the lever arm in the first direction with respect to the substrate. In this regard, the platform may be attached to the substrate at a first location and the lever arm may be attached to the platform at a second location and to the substrate at a third location, with the third location being between the first and second locations when the platform is in a non-tilted orientation with respect to the substrate.
In one embodiment, the lever arm comprises an A-frame structure. The base of the A-frame structure may be attached to the substrate by one or more flexible members. The flexible member(s) is/are configured to permit pivoting of the A-frame structure about its base in at least the first direction with respect to the substrate. In this regard, the flexible member(s) may permit the A-frame structure to be rotated in only a clockwise/counterclockwise direction about an axis parallel with the plane of the substrate while restricting rotation of the A-frame structure about an axis perpendicular to the substrate. The apex of the A-frame structure may be coupled to the platform by the second compliant member or the A-frame structure may include a rigid member that extends from the apex of the A-frame portion of the A-frame structure that is then coupled to the platform by the second compliant member.
In order to achieve pivoting of the lever arm, the MEM system may include an actuator microstructure that is formed on the substrate. The actuator microstructure is coupled to the lever arm and operable to effect pivoting of the lever arm in at least the first direction with respect to the platform. In this regard, a laterally moveable output (i.e., an output that moves generally parallel with the plane of the surface of the substrate) of the actuator microstructure may be coupled with the lever arm by a tether. One end of the tether is attached to the moveable output of the actuator microstructure and the other end of the tether is attached to the lever arm between the second and third locations. When the actuator microstructure is operated, the tether pulls the lever arm thereby pivoting the lever arm with respect to the substrate.
In order to generate sufficient force, the actuator microstructure may be comprised of a plurality of separate actuators such as, for example, a plurality of electrostatic actuators operable in response to a control voltage applied across terminals thereof. The laterally moveable outputs of the separate actuators may be coupled together by a laterally moveable yoke formed on the substrate. In this regard, the tether is attached to the yoke so that the combined force of the separate actuators is applied via the tether to the lever arm. Since the lateral movement that may be achieved with an electrostatic actuator or the like may be small, the MEM system may also include a displacement multiplier between the yoke and the tether. The displacement multiplier amplifies the lateral movement of the yoke into larger lateral movement of the tether thereby achieving substantial pivoting of the lever arm with only small lateral movement of the yoke.
Prior to use of the MEM system, it may be desirable to inhibit unintended movement of the platform which might cause damage to the platform or other components of the MEM system. In this regard, the MEM system may include one or more fuses securing the platform to the substrate. Upon application of an appropriate voltage across the fuse(s), the fuse(s) are melted or vaporized thereby freeing the platform from the substrate to be lifted and tilted. The fuse(s) may also be removed using a laser cutter or other similar device. The MEM system may also include one or more pre-stressed elevators attached to the substrate and in contact with platform or lever arm. Upon melting/vaporization or cutting of the fuse(s), the pre-stressed elevator(s) curl upward thereby elevating the platform to a predetermined initial height from the substrate where it can be further lifted and also tilted by the lever arm.
According to another aspect of the present invention, a MEM system includes a substrate, a platform formed on the substrate and first and second lever arms formed on the substrate. The platform includes first, second and third attachment points. The platform may be attached to the substrate at the first attachment point of the platform. The first lever arm is attached to the platform at the second attachment point. The second lever arm is attached to the platform at the third attachment point thereof. In this regard, the first and second lever arms may be attached to the platform by compliant members (e.g., springs) and the platform may also be attached to the substrate by a compliant member (e.g., a spring). The first and second lever arms are also pivotably attached to the substrate at first and second anchor points, respectively, on the substrate. The first attachment point is located on the same side of an imaginary line intersecting the second and third attachment points as the first and second anchor points are located when the platform is in a non-tilted orientation with respect to the substrate. In this regard, the first attachment point may be located between the imaginary line intersecting the second and third attachment points and another imaginary line intersecting the first and second anchor points to achieve generally larger changes in the angle of inclination of the platform with respect to the substrate than the angle through which the first and second lever arms are moved. Alternatively, the first attachment point may be located on the opposite side of the imaginary line intersecting the first and second anchor points to achieve generally smaller changes in the angle of inclination of the platform with respect to the substrate than the angle through which the first and second lever arms are moved. It will be appreciated that the latter location of the first attachment point allows for more precise control of the angle of inclination of the platform in comparison with the former location.
The first and second lever arms are separately pivotable about the first and second anchor points, respectively, by unequal angular amounts to tilt the platform with respect to the substrate with at least two degrees of freedom. In this regard, the MEM system may include first and second actuator microstructures formed on the substrate. The first actuator microstructure is coupled (e.g., by a tether) to the first lever arm and is operable to effect pivoting of the first lever arm with respect to the substrate. The second actuator microstructure is coupled (e.g., by a tether) to the second lever arm and is operable to effect pivoting of the second lever arm with respect to the substrate. The first and second actuator microstructures may be electrostatic actuators that are operable in response to control voltages applied across terminals thereof. In this regard, the platform may be tilted with respect to the substrate with only one degree of freedom by applying the same level control voltage across the terminals of the first and second actuator microstructures. By applying unequal control voltages across the terminals of the first and second actuator microstructures, the platform may be tilted with two degrees of freedom. It is also possible to fabricate the MEM system with the first and second lever arms having non-symmetric geometries (e.g., differing lengths or locations where the tethers are attached) so that application of equal control voltages achieves tilting of the platform with two degrees of freedom.
According to a further aspect of the present invention, a MEM system includes a substrate, a platform formed on the substrate, one or more tethers formed on the substrate, and one or more compliant members formed on the substrate pivotably attaching the platform to the substrate. The tether (or each tether, if more than one) is laterally moveable with respect to the substrate in a direction parallel with a lengthwise axis of the tether and is coupled at one end thereof to the platform by a compliant member. The compliant member(s) pivotably attaching the platform to the substrate is/are configured to permit the entire platform to be elevated from the substrate. In this regard, the platform may include a frame portion extending laterally therefrom, with the frame portion being attached at a first point thereof by a first compliant member to the tether and pivotably attached to the substrate at second and third points thereof by second and third compliant members. The first, second and third compliant members may comprise segmented torsional springs. The second and third points of the frame portion may be located between the first point where the frame portion is attached to the tether by the first compliant member and an end of the tether opposite the end of the tether attached to the frame portion. In response to lateral movement of the tether away from the platform, the platform swings up and away from the platform. Likewise, in response to lateral movement of the tether towards the platform, the platform swings down towards the substrate.
According to yet another aspect of the present invention, a microelectromechanical system includes a substrate, a platform formed on the substrate, and first and second lever arms also formed on the substrate. The first lever arm is attached to the platform by one or more compliant members and is also pivotably attached to the substrate at a first anchor point on the substrate. The second lever arm is attached to the platform by one or more compliant members and is also pivotably attached to the substrate at a second anchor point on the substrate. The platform is not attached to the substrate (other than indirectly through the lever arms). The first and second lever arms are simultaneously pivotable about the first and second anchor points, respectively, in at least a first direction (e.g., clockwise or counter-clockwise) by equal angular amounts to incline the platform in at least the first direction. The first and second lever arms are also separately pivotable about the first and second anchor points, respectively, by unequal angular amounts to tilt the platform with respect to the substrate with at least two degrees of freedom.
These and other aspects and advantages of the present invention will be apparent upon review of the following Detailed Description when taken in conjunction with the accompanying figures.